1. Field of the Invention
The present invention relates to an image pick-up apparatus, an image processing apparatus and a method of correcting chromatic aberration of a lens, which are suitable for use in a video camera or a digital still camera, for example. Specifically, the present invention relates to satisfactorily correcting chromatic aberration of a lens which is caused when image light which passes through an image pick-up lens.
2. Description of the Related Art
For example, in an image pick-up apparatus to pick up a color picture using an image pickup unit including a plurality of image pickup devices or image pickup tubes, there have been proposed hitherto various methods of correcting a registration of pictures among a plurality of image pickup units using an electrically correcting unit (for example, refer to patent references 1 through 3).
However, each of the above described art relates to the image pick-up apparatus which uses a plurality of image pickup devices and image pickup tubes, and is different from an image pick-up apparatus to pick up a color picture by providing an optical color filter on an image pickup surface of, for example, one piece of image pickup device. Moreover, there is no description provided with respect to the correction of chromatic aberration of a lens in the image pick-up apparatus to pick up a color picture by providing the optical color filter on the image pickup surface of, for example, one piece of image pickup device.
On the other hand, as means to prevent a picture quality degradation such as color blurring and a resolution degradation caused by magnification chromatic aberration, there is known technology in which a video signal of each color of R, G and B taken out from a CCD (image pickup device) is temporarily stored in an individual field memory respectively; further each picture is magnified or reduced by individually performing a vector transfer of the whole of each field memory based on a drive state of an image pick-up lens such as a zoom focal length and a focal position; thereafter, R, G and B are again combined, and thereby, a color smear which is generated by an image pick-up lens of a video camera is corrected (for example, refer to a patent reference 4).
However, when the apparatus is used performing camera shake correction, for example, sufficient correction can not be performed. In other words, when the vector transfer is performed individually to the whole of each field memory in the above described apparatus, the center is made to coincide with a light axis of an image pick-up lens; however, when the camera shake correction is performed, a position of the light axis is moved and it becomes difficult to make the center coincide with the light axis.                [Patent reference 1] Japanese Patent No. 2552741        [Patent reference 2] Japanese Patent No. 2922905        [Patent reference 3] Japanese Published Examined Patent Application No. H6-5959        [Patent reference 4] Japanese Published Unexamined Patent Application No. H5-3568        
For example, a miniaturization is rapidly advanced in a video camera or a digital still camera, and the miniaturization is also demanded with respect to an image pick-up lens. For this reason, regarding the miniaturization of the image pick-up lens, conventional one which uses a number of combined lenses is replaced with miniaturized one including one piece or a small number of lenses. Moreover, a lens having a smaller diameter replaces a lens having a larger diameter for the miniaturization. As an alternative, less expensive material of a lens is used for a price reduction.
However, in the case where such miniaturized image pick-up lens is used, it becomes difficult to sufficiently prevent the picture quality degradation such as so-called chromatic aberration generated in the lens. In other words, since a refractive index in a lens is different depending on each wavelength of red (R), green (G) and blue (B) which is separated by, for example, a spectroscopic filter in an optical lens, there occurs such a phenomenon that an image of red (R) is focused outside the image of green (G) and an image of blue (B) is focused inside the image of green (G), as shown in FIG. 5 for example. Therefore, even if a subject for image pick-up is formed of, for example, white and black only, there has been a problem in which color blurring (color smear) is generated in the edge of a picture.
Therefore, in order to prevent the picture quality degradation such as the color blurring and the resolution degradation caused by such magnification chromatic aberration (also, called as horizontal chromatic aberration), conventionally a large number of lenses are combined to perform the correction inside the image pick-up lens; however it has become difficult to fully prevent such picture quality degradation with the image pick-up lens which is miniaturized as described above. In order to deal with the above problem, such apparatus as is disclosed in the above mentioned patent reference 4 has been proposed as means which prevents the picture quality degradation such as the color blurring or the resolution degradation by the magnification chromatic aberration.
In other words, in the apparatus disclosed in the patent reference 4, the video signal of each color of R, G and B which is taken out from the CCD (image pick up device) is once converted into digital data; the data is stored temporarily in the individual field memory respectively; further each picture is magnified or reduced by performing individually the vector transfer on a pixel stored in each field memory based on the drive state of the image pick-up lens such as the zoom focal length and the focal position; and the color smear generated in the image pick-up lens of the video camera is corrected subsequently by combining R, G and B again.
On the other hand, when image pick-up is performed by holding, for example, the above mentioned compact video camera or digital still camera by hand, there is a possibility of causing a trouble such as picture shaking due to so-called camera shake. Accordingly, a so-called camera shake correction apparatus is equipped in the compact video camera or the digital still camera for the purpose of eliminating such troubles as the picture shaking. FIG. 6 shows a block diagram of a video camera or a digital still camera in which such camera shake correction apparatus is equipped.
In FIG. 6, image light from a subject (not shown) is focused on an image pickup surface of an image pickup unit 151 including a CCD, a CMOS sensor and the like through an image pick-up lens 150, and is converted into an electrical picture signal including, for example, an intensity signal (Y) and two color-difference (Cb, Cr) signals. This picture signal is supplied to a camera signal processing circuit 152, and signal processing such as so-called γ-correction is performed to form a conventional picture signal which is used for a general-purpose video apparatus.
Further, in order to detect a so-called camera shake, hereupon two gyroscopic sensors 153P and 153Y, for example, are used, and angular velocities generated by the camera shake in the pitch direction and in the yaw direction are detected. Further, a zoom focal length of the image pick-up lens 150 which is operated by, for example, a user is detected by the image pick-up lens 150. In addition, it is possible to use an operational signal from a manual operation input unit 154, for example, by the operation of the user to detect the zoom focal length.
Then, signals of the angular velocity detected by the gyroscopic sensors 153P and 153Y are supplied to high-pass filters (HPF) 155P and 155Y to remove a direct-current component, and also, the data of the above mentioned zoom focal length are supplied to a table 156 to obtain a necessary operation coefficient from the data, and this operation coefficient is supplied to multipliers 157P and 157Y to multiply signals from the high-pass filters 155P and 155Y by the operation coefficient. Furthermore, output signals from the multipliers 157P and 157Y are respectively supplied to integrators 158P and 158Y.
Accordingly, angle information on the image pick-up lens 150 which is fluctuated by the camera shake is taken out from the integrators 158P and 158Y. Then, this angle information of the camera shake is supplied, for example, to the image pickup unit 151 through limiter circuits 159P and 159Y, and a position where the picture signal is taken out from the image pickup unit 151 is controlled. In other words, a larger image pickup surface than a size of an original picture is provided, for example, in the image pickup unit 151, and a required picture is taken out from inside the image pickup surface so as to cancel out the fluctuation by the camera shake.
Thus, in the case where the compact video camera, digital still camera or the like is used, the so-called camera shake correction is performed. In addition, as means for performing the camera shake correction, such a method of storing all the picture signals picked up by the image pickup unit 151 in a memory 160 and of controlling a position to read out the picture signal from this memory 160, and a method of shifting and correcting a position of a part of lenses in the image pick-up lens 150 have also been performed other than the control of the position to take out the picture signal from the above mentioned image pickup unit 151.
Further, as means to take out the angle information of the image pick-up lens 150 which is fluctuated by the camera shake, other than the means which uses the above mentioned gyroscopic sensors 153P and 153Y, the picture signal from the image pickup unit 151 is made to be stored in a frame memory 161 as shown in FIG. 7 for example, and picture signals prior to and subsequent to this frame memory 161 are compared in a comparing circuit 162 so that the angle information on the camera shake can also be computed from a movement of a picture such as a background thereof. In addition, this computed angle information on the camera shake can be used in all of the above mentioned camera shake correction means.
However, when it is tried to perform the correction of the picture quality degradation such as the color blurring or the resolution degradation caused by the magnification chromatic aberration using the apparatus disclosed, for example, in the above described patent reference 4 while performing such camera shake correction, the sufficient correction can not be performed. In other words, when the vector transfer is performed individually to the whole of each field memory in the above described apparatus, the center thereof should coincide with the light axis of the image pick-up lens; however when the camera shake correction is performed, the position of the light axis is moved and it becomes difficult to make the center coincide.
Accordingly, conventionally the correction of the picture quality degradation caused by such as chromatic aberration is not performed concurrently with the correction of the camera shake. However, in case of a conventional model which has a small number of pixels, the picture quality degradation such as the chromatic aberration becomes less conspicuous particularly when an image is picked up with the camera shake correction. However, an increase in the number of image pick-up pixels has been demanded in recent years and as a result, an influence of the picture quality degradation such as the chromatic aberration has become noticeable in all situations.
This application is made in view of the above and the problem to be solved is that with a conventional means, the problem of the picture quality degradation such as the color blurring or the resolution degradation caused by the magnification chromatic aberration occurs due to a miniaturization of an image pick-up lens and the like; it becomes difficult to fully prevent such picture quality degradation only using the image pick-up lens; and further, there has not been proposed means to satisfactorily realize such correction in an image pick-up apparatus to pick up a color image by providing an optical color filter on an image pickup surface of, for example, one piece of image pickup device.